Process for defibering wet strength paper by multiple alkaline cooks



Feb. 4, 1969 P JR 3,425,897

PROCESS FOR DEFIBERING WET STRENGTH PAPER BY MULTIPLE ALKALINE COOKS Filed Nov. 22. 1965 INVENTOIR filoms L. Mue mg Ia ATTORNEYS United States Patent 3,425,897 PROCESS FOR DEFIBERING WET STRENGTH PAPER BY MULTIPLE ALKALINE COOKS Thomas L. Murphy, Jr., Columbia, Miss., assignor, by direct and mesne assignments, of thirty-three percent to Bluff Creek Industries, Vancleave, Miss., a corporation of Mississippi, eleven and two-thirds percent to Bryan Bell and three and one-third percent to Rubie C. Bell, both of New Orleans, La.

Filed Nov. 22, 1965, Ser. No. 508,966 US. Cl. 162--8 13 Claims Int. Cl. D21c /02 ABSTRACT OF THE DISCLOSURE Waste, wet strength, resin-impregnated paper is defibered for reuse by first cooking it with caustic solution under pressure for about one to five hours and then releasing the pressure, diluting the mass to pulping consistency and completing the defibering with a further alkaline treatment under milder conditions with agitation of the mass.

The present invention relates to a process for reclaiming wet strength paper and more particularly to the conversion of single ply amide resin treated kraft paper into discrete cellulose fibers suitable for addition to a paper furnish, for bleaching or any other treatment to which the original kraft pulp could have been subjected.

The defibering of wet strength resin impregnated paper stock has been a problem long defying successful solution by the pulp and paper industry. The resins usually employed are of the thermosetting aminoplast variety, that is, urea-formaldehyde or melamine-formaldehyde resins which are preferably modified to a cationic nature, so that they can be added to the heater or head box of a paper machine and can be quantitatively absorbed by the negatively charged cellulose fibers. The absorbed resins irreversely cure during the drying of the sheet and the wet strength of the sheet is increased several fold and dry strength characteristics such as rub resistance and tensile and bursting strengths are also improved by the presence of these heat cured resins.

The resin impregnated wet strength paper is thus incapable of being simply defibered by beating action alone, since it completely resists dissolution by water, even when combined with mechanical beating action. Thus, the production of wet strength paper differs considerably from the normal manufacture of paper, wherein the considerable waste that results from trimming, roll changeover and mechanical breakdown at the dry end of a paper machine cannot be simply returned to the beater or head box of the machine. The present practice is simply to collect all waste trimmings and to burn them. This difference has always economically precluded the use of wet strength paper in the manufacture of bags and paper sheeting intended for ordinary wrapping and packaging and has been restricted to special uses such as ice bags, ice cream bags and the like.

It is, therefore, an object of the present invention to provide an economical process for defibering wet strength paper.

A further object is the provision of an economical and efficient method of removing heat cured resins from wet strength waste paper by treating such materials under controlled conditions without the need for excessive chemical, energy or manipulation of the material.

Another object of the present invention is the provision of a process for reclaiming wet strength waste such as used wet strength paper or trim or broke, which includes a simple and highly eflicient recovery system 3,425,897 Patented Feb. 4, 1969 whereby the fiber is recovered for reuse without any substantial deterioration of the fiber.

A still further object is to provide a convenient process for the continuous reprocessing of wet strength trim or waste so as to make economically feasible the application of wet strength resins to kraft paper intended for general usage.

Other objects and advantages of the invention will become readily apparent as the same becomes better understood by reference to the following detailed description of the invention in both its general aspects and the specific embodiments as described in relation to an example and the attached figure, which is a schematic representation of general apparatus suitable for performing the method.

The above objects are accomplished according to the invention by a defibering process which involves an essential step of cooking the waste wet strength paper under alkaline conditions with direct addition of steam usually in a digester with caustic soda. For convenience of operation, the waste paper should be divided into. small pieces, e.g. 3" squares by a paper shredder 2 for ease of conveyance and to present the paper in a manner more readily digested by the alkaline reagent. After sufiicient shredded pieces for one cooking have been air conveyed through conduit 4- into cyclone hopper 6, valve 8 is opened and the pieces fall by gravity into digester 10. The digester, which is rated for lbs. steam pressure, is filled to about 20% capacity and then valve 12 is opened and caustic soda drains into the digester from caustic soda storage tank 14. Valves 8 and 12 are then closed and valve 16 is opened and steam is added through conduit 18 until the desired temperature is obtained and is continuously metered in over the complete cooking cycle to maintain this temperature After the cooking is completed, the fiber is then expelled from the bottom of the digester through blow valve 20 through conduit 22 into blow tank 24 having exhaust vomit stack 26. From the pulp holding tank, the substantially defibered pulp is transferred, unwashed, to pulper 28 by positive displacement pump 30 through conduit 32. Fresh water is added to dilute the pulp to normal pulping consistency, e.g. 34%. Caustic black liquor is added and pulping is initiated by opening recirculation valve 344 and recirculating the pulp through recirculation conduit 36 by means of pump 38. The contents of the pumper are also agitated by means of impeller 40 driven by electric motor 42. When complete defibering has occurred, recirculation valve 34 is closed and valve 44 is opened and the defibered stock is pumped to brown stock Washers for conventional handling and processing.

The parameters of the cooking step cannot be exactly defined since, of course, they depend on the nature of the resin, the amount of resin impregnated into the paper and the temperature at which it was cured. Furthermore, the time and temperature of the treatment vary inversely and both depend on the concentration of the alkaline reagent. The preferred procedure is to dilute the shredded pieces to a consistency of 15 to 25%, preferably 20% and to add 5 to 20% caustic on a dry basis to the diluted pulp which assures breaking of the resin in a reasonable time without degradation of the fiber. Under these conditions, the temperature need only be raised to 120 C. to C. for about 1 to 5 hours, .160 C. for 3 hours being an optimum process. The final defibering of the pulp is conducted under very mild conditions at temperatures of only 25 to 50 C. for short times for about 5 to 25 minutes with caustic black liquor of about 2 to 5% dry basis. This can simply be effected by additional caustic to the residual caustic that remains after the digesting step.

The process has wide applications to a wide variety of papers including both bleached and unbleached kraft and sulphite pulps that have been impregnated with wet strength resin. The process is also applicable to any of the synthetic wet strength resin impregnated papers and preferably, the amino condensation resins including polyureas, polyamides, melamine-formaldehyde and urea or thioureaformaldehyde paper resins. This is intended to include the modification of the basic resins to form cationic resin molecules or cationic colloids by means of mono or polyfunctional organic nitrogen bases, amino acids, such as glycine, proteins, such as gelatin or by sulphites of inorganic or organic bases or diglycolic acid or its salts.

The preferred materials are urea-formaldehyde resins modified by water soluble polyfunctional organic nitrogen bases, such as alkaline polyamides of the formula in which n is two or more and x is one or more, such as ethylenediamine and 1,3-propy1enediamine and polyalkylenepolyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine; the corresponding polypropylene-polyamines and polybutylenepolyamines; also guanidines, biguanides, the guanylureas and the salts thereof; condensation products of alkylenepolyamines, such as the above with halohydrins such as p-dichlorhydrin, epichlorhydrin and the like; monoalkylolamines; dialkylolamines, trialkylolamines, and the like; and the water-soluble condensation products thereof with aldehydes such as formaldehyde. The amount of water-soluble polyfunctional organic nitrogen base used may vary widely. Generally, from about 3% to about 44% of the polyfunctional base by weight based on the urea is preferred. The polyalkylenepolyamines are the preferred polyfunctional bases for the purposes of this invention.

The invention is now illustrated, but is not intended to be limited by the following specific example of processing waste wet strength paper according to the invention, it being recognized that various modifications can be made in both the apparatus and method of operation without deviating from the scope of the invention.

Example Waste urea formaldehyde epichlorohydrin alkaline polyamine impregnated wet strength paper is shredded so that the individual pieces do not exceed 3" by 3" and these shredded pieces are then blown to cyclone hopper and then fall into the digester by gravity. After the digester is filled within 20% of its capacity, solution of caustic soda is injected into the digester until the mass is diluted to a consistency of approximately The caustic soda is added to an amount of 10% basis dry paper. The digester is then closed and heated by direct addition of steam up to a temperature of about 160 C. and held at this temperature for about 3 hours by continuously metering steam into the digester. During this cooking period 8.75% of caustic is consumed as determined by chemical residual. The fiber is then expelled into the blow tank for holding and from there is transferred, unwashed, to a pulper. Fresh water and additional caustic are added to the pulper to bring the pulp to a consistency of 34% and the caustic to 4% on a dry basis. The material is pulped at C. for about 5 minutes with circulation plus agitation and can then be transferred to brown stock washers or to storage for conventional handling and processing. A sample of pulp was centrifuged to about 30% solids and yield and KMnO measured. The yield was 86.0% (basis paper) and the KMnO No. was 142/25 ml.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A process for reclaiming wet strength paper comprising treating the paper under alkaline conditions at elevated temperature and under pressure for about one to five hours, releasing the pressure, and then completing the defibering by diluting the mass to pulping consistency and further treating it with caustic solution under milder conditions at a temperature of about 25 C. to about 50 C. and a sodium hydroxide concentration of about 2 to 5% on a dry basis with simultaneous agitation and circulation of the mass.

2. A process according to claim 1 in which the temperature of the initial treatment is from about C. to 180 C. and the treatment is continued for about 1 to 5 hours.

3. A process according to claim 1 in which the paper in the initial treatment is diluted to a consistency of 15-25% and the alkaline reagent is present in an amount of 5 to 20% on a dry basis.

4. A process according to claim 1 wherein the paper in the initial treatment is diluted to a consistency of 20%, 10% sodium hydroxide caustic is added thereto on a dry basis and this mixture is contacted with direct steam to raise the temperature to about C. and this temperaure is maintained for about 3 hours.

5. A method according to claim 1 wherein the paper contains an amino condensation wet strength resin.

6. A process according to claim 5 wherein the resin is a melamine-ureaor thiourea formaldehyde wet strength resln.

7. A process according to claim 6 wherein the resin is modified to a cationic nature.

8. A process according to claim 7 wherein the resin is modified with a polyamine.

9. A process according to claim 8 wherein the resin is modified with an epichlorohydrin-polyamine reaction product.

10. A process according to claim 1 wherein preparatory to the alkaline treatment, the paper is shredded into pieces not greater than about 3" in any dimension.

11. A process according to claim 1 wherein the paper is single-ply kraft wet strength paper.

12. A process according to claim 1 wherein the mass after the initial treatment is diluted to a pulp consistency of about 34% 13. A process for the complete defibering of waste, trim or broke amine-resin treated wet strength single-ply kraft paper comprising the steps of shredding said paper into pieces not larger than 3" in any dimension, diluting said pieces to a consistency of about 20% and contacting them under pressure with 10% sodium hydroxide on a dry basis and directly with steam until a temperature of about 160 C. is attained and maintaining that temperature for about 3 hours, releasing said pressure and diluting the treated paper with water to a consistency of 34% and adjusting the sodium hydroxide to about 4% on a dry basis and pulping this mixture at a temperature of 35 C. with recirculation and agitation of the mixture and then recovering a completely defibered pulp.

References Cited UNITED STATES PATENTS HOWARD R. CAINE, Primary Examiner. 

